Fixture for making glass-to-metal seals and method of making the same



NOV. 24, 19m A. T. JOHNSON 3,542,576

FIXTURE FOR MAKING GLASS-TO-METAL SEALS AND METHOD OF MAKING THE SAMEFiled OC'L. 4, 1967 22., 23,24,& 25

INVENTOR Ari'hur T. Johnson United States Patent FIXTURE FOR MAKINGGLASS-TO-METAL SEALS AND METHOD OF MAKING THE SAME Arthur T. Johnson,Providence, R.I., assignor to GTI Corporation, a corporation of RhodeIsland Filed Oct. 4, 1967, Ser. No. 672,846

Int. Cl. B4411 1/14; C04!) 41/06; C03c 27/02 US. Cl. 117-2 9 ClaimsABSTRACT OF THE DISCLOSURE A high temperature ceramic fixture isdisclosed for employment in holding metal and glass components in properposition for fusing of glass-to-metal seals therebetween. The life ofthe fixture and the quality of the glassto-metal seals are improved by aunique method of depositing a uniformly adherent coating of carbon onthe fixture at relatively low temperatures. The carbon-coated ceramicfixture is more durable and its coating can be periodically replenishedduring usage without the necessity of refiring or replacing thefixtures.

The present invention relates to an improved fixture for holding metaland glass components or the like in proper position during fusing toproduce metal-to-glass seals therebetween, and more particularly to aceramic fixture, having a protective coating wherein the coating islonger lived and is replenishable.

In the past, a number of such fixtures have been proposed. In oneinstance the fixture has been fabricated from solid carbon or graphite.Although such fixtures are useful in some applications, at elevatedtemperatures they tend to crack and require frequent replacement. Thesolid carbon or graphite fixtures moreover are fragile and difficult tohandle in use.

Similar fixtures fabricated entirely from ceramic ma. terials also havebeen utilized. These fixtures suffer from the disadvantages that thefused glass or the like tends to adhere thereto.

Attempts have been made to remedy this disadvantage of ceramic fixturesby depositing a coating of carbon on the ceramic fixtures. In general, amore satisfactory ceramic fixture has been produced. The carbon coating,however, according to previous applicative methods has been deposited asa relatively thin coating and has been baked on the ceramic fixtures atelevated temperatures in special atmospheres to prevent oxidation of thecoating. In practice, it has been found that the life of priorcarbon-coated ceramic fixtures has been relatively short and that thequality of the fused components has been impaired. The application ofcoating to prior carboncoated fixtures requires special equipment andthe coating cannot be replenished by users of the fixtures.

Usage of previously proposed fixtures for the indicated purposes hasalso resulted in excessive numbers of rejects among the fused componentsas a result of breakage or leakage.

In my copending application Ser. No. 672,919 filed Oct. 4, 1967, Idisclose an improved fixture for making glassto-metal seals whichgenerally overcomes these problems of the prior art. The presentinvention is a further improvement.

I overcome the disadvantages of the prior art described above byproviding a ceramic fixture having a protective coating therein whichexhibits an extended life under customary conditions of usage of manytimes that of known ceramic fixtures and superior to that of fixturesmade according to my copending application mentioned above. Thecharacter of the protective coating which my invention enables one toapply to ceramic fixtures improves 3,542,576 Patented Nov. 24, 1970 iceconsiderably the quality of the finished fused components or devices. Myinvention permits the production of fused devices with a smaller numberof rejects resulting from breakage or of imperfect seals.

Briefly, my invention provides improved coated ceramic fixtures for thepurposes described and also improved methods for coating the fixtures,for example with a carbonaceous material. Thus, a preferred form of mynovel method involves a cleaning and preparing the surface of theceramic fixtures, coating the ceramic fixture with a carbonaceous dryingoil such as linseed oil, baking the coated fixtures at a relatively lowtemperature until dry, applying to the baked fixtures a graphiticsuspension or the like, followed by a coating of carbonaceous dryingoil, baking the fixture a second time at low temperature and sprayingthe fixture while still hot With a final coating of graphite. My novelmethod not only produces more durable ceramic fixtures, but also thecarbon coating thereof can be applied in a simple manner. The use ofhigh temperature furnaces and special firing atmospheres is avoided.Moreover, the life of the coating applied to the fixture in accordancewith my invention can be prolonged by periodic application of thegraphitic coating material throughout the useful life of the fixtures.

I accomplish these desirable results by providing a coated ceramicfixture for holding components in proper position during fusing of saidcomponents to join said components, said fixture comprising a ceramicbase member, a first coating of polymerized. drying oil uniformlyadhered to the surface of said base member, a second protective coatingof graphitic material uniformly covering said first coating, a thirdcoating of polymerized drying oil and a fired coating of graphiticmaterial to protect the surfaces of said components when engaged by thefixture.

I also desirably provide a coated ceramic fixture wherein each of saidcoatings contain a carbonaceous material.

I also desirably provide a method for coating a ceramic fixture, saidmethod comprising the steps of coating said fixture with a drying oil,baking said fixture to dry said oil, applying a suspension ofcarbonaceous material, and thereafter a coating of drying oil, bakingsaid fixture to dry the same, removing said fixture from said bakingstep and applying a suspension of carbonaceous material to the fixturewhile hot.

I also desirably provide a method for coating a ceramic fixture whereinsaid fixture is immersed in an aqueous solution of sulphuric acid andrinsed prior to coating with a drying oil.

I also desirably provide a method. for coating a ceramic fixture whereinthe final application of carbonaceous material is accomplished byspraying while said fixture is still hot and the sprayed fixture ispermitted to dry at room temperature.

I also desirably provide a method for coating a ceramic fixture whereinthe final coating of said fixture is replenished periodically during useof said fixture.

During the foregoing discussion, various objects, features andadvantages of the invention have been set forth. These and otherobjects, features and advantages of the invention together withstructural details thereof will be elaborated upon during theforthcoming description of certain presently preferred embodiments ofthe invention and presently preferred methods of practicing the same. Inthe accompanying drawings l[ have shown certain presently preferredembodiments of the invention and have illustrated certain presentlypreferred methods of practicing the same, wherein:

FIG. 1 is a longitudinally sectioned viewof a typical ceramic fixturecoated in accordance with my invention; and

FIG. 2is an enlarged sectional view of a portion of the fixture shown inFIG. 1.

Referring now more particularly to the drawings the exemplary form of myinvention shown therein includes a coated fixture 10, which is useful insupporting, for example, metal and glass components 12 and 14 during thefusing process to form a glass-to-metal seal 16 therebetween. Thus, thefixture includes recess 18 shaped generally to receive the glasscomponent 14 and recess 20 shaped to receive likewise the metalcomponent 12.

The fixture 10 as better shown in FIG. 2 is provided with a firstbaked-on layer 22 of linseed or other drying oil, a second coating 23 ofcarbon, graphite or other carbonaceous protective material, a thirdcoating 24 of linseed or other drying oil and a final sprayed-on layer25 of carbon, graphite or similar carbonaceous material. The layer 24provides a suitable base surface to which the sprayed-on coating 25 canproperly adhere. On the other hand the final layer 25 protects andextends the life of the baked-on uniformly adherent coating layers 22and 23, and the four coating layers 22-25 provide a proper surface ofengagement with juxtaposed portions of the metal and glass components12, 14.

It has been found that the use of my multiple-coating ceramic fixture10, including the coating layers 22, 23, 24 and 25 produces a superiorglass-to-metal seal 16 and does not mar the adjacent surfaces of themetal and glass components 12, 14 in contrast to previously proposedfixtures. I have also found during usage of the fixtures such as thefixture 10 that the outer carbonaceous layer 25 can be periodicallyrenewed without the use of firing or baking or special gaseousenvironments or the like. I have found, on the contrary, that I canperiodically replenish the outer coating 25 on the fixture 10 as byspraying or dipping or the like to renew the outer coating layer 25followed by drying the newly applied layer 25 for a brief interval atroom temperature and without a special atmosphere. Thus the outercoating 25 can be replenished periodically by the user and without theuse of special equipment.

Desirably I clean the fixture prior to coating by dipping the same in acleaning solution including desirably about 50 volume percent sulphuricacid (H 50 and 50 volume percent water (H O). The cleaning solutionpreferably is maintained at a temperature of about 90 F.il0 F., and thefixture is permitted to remain therein for about 15 minutes.

Following this interval, I desirably remove the fixture from thelast-mentioned solution and immerse and rinse the fixture thoroughly indistilled water.

After removing the fixture from the rinse, I coat the same with rawlinseed oil and then bake at 250 F. until dry (about 15 minutes). I thencoat the dried coated fixture with a graphitic suspension or asuspension of other suitable carbonaceous material and then with anothercoating of raw linseed oil. The fixture is again baked, this time atabout 300 F. for 8-10 hours. The fixture is removed from the furnace andsprayed while hot with two successive coatings of graphitic suspension.Preferably the coating is allowed to air dry for an interval of minutesuntil dry. Preferably, I formulate the graphitic suspension in thefollowing proportions: 25 grams of concentrated graphite (Aquadag) in100 cc. of water. Aquadag is a trade name for a finely divided collodialdispersion of graphite available from Acheson Colloids Co.

The several steps of my method together with the preliminary surfacepreparational steps produces a uniformly adherent coating on the fixtureof the metal from the drying oils and the graphitic suspension. Thiswell adhered coating protects the surfaces of the fixture and moreimportantly those surfaces of the metal and glass components 12, 14,which are engaged by the fixture 10. Most importantly the adheredcoating provides a proper base to receive the second or outercarbonaceous coating applied in the final step of my method. This latterprotective coating otherwise would not adhere to the bare ceramicsurface of the fixture 10.

The several drying oil coatings as Well as the carbonaceous layers canbe applied by brushing or dipping a graphitic suspension on the coatedfixture or by analogous methods.

In any event it will be seen that the final protective coating 25 thusapplied to the fixture 10 can be periodically renewed without the use ofspecial equipment or without the necessity of returning the fixtures tothe manufacturer for reprocessing. Discarding of used fixtures istherefore frequently avoided.

During usage of the fixture, the outer coating layer of the fixturedesirably is replenished periodically. This is accomplished. byreapplying the outer coating layer 25 as by spraying and drying in themanner described above. Where the fixture is employed for the fusing ofglass and metal components to effect a glass-to-metal seal therebetween,the fixture desirably is recoated as by spraying after every 15 passesthrough the furnace employed for fusing the glass and metal parts.

From the foregoing it will be apparent that novel and efficient forms offixtures for making glass-to-metal seals have been described herein.While I have shown and described certain presently preferred embodimentsof the invention and have illustrated presently preferred methods ofpracticing the same, it is to be distinctly understood that theinvention is not limited thereto but may be otherwise variously embodiedand practiced.

I claim:

1. A coated ceramic fixture for holding glass and metal components inproper position during fusing of said components to join saidcomponents, said fixture comprising a ceramic base member, a firstprotective coating of polymerized carbonaceous drying oil uniformlyadhered to the surface of said base member, a second protective coatingof graphitic material uniformly covering said first coating, a thirdprotective coating of polymerized carbonaceous drying oil adhered tosaid second coating and a final coating of graphitic material coveringthe third coating to protect the surface of said components when engagedby the fixture.

2. A method for coating a ceramic fixture, said method comprising thesteps of applying to said fixture a first coating of carbonaceous dryingoil, heating the coated fixture to dry said coating, applying to saidfirst coating a suspension of graphitic material, and thereafter asecond coating of said drying oil, baking the coated fixture to adheresaid graphitic material and said second coating of carbonaceous dryingoil to said first coating, and applying a final protective coating ofgraphitic material to said adhered coatings.

3. The method according to claim 2 wherein said fixture is immersedsuccessively in an aqueous solution of sulphuric acid and a water rinseprior to applying said first coating.

4. The method according to claim 3 wherein said fixture is sprayed witha graphitic suspension immediately after the baking step while thefixture is still hot.

5. The method according to claim 2 wherein said fixture is baked at atemperature of about 300 F. for an interval of about 8-10 hours.

6. The method according to claim 5 wherein said fixture is baked in anair atmosphere.

7. The method according to claim 2 wherein the final application ofgraphitic material is accomplished by spraying immediately after bakingthe coated fixture and the sprayed fixture is permitted to dry at roomtemperature.

8. The method according to claim 7 wherein said sprayed fixture ispermitted to dry for an interval of about 30 minutes in an airatmosphere.

9. The method according to claim 2 wherein the final coating of saidfixture is replenished periodically during use of said fixture.

(References on following page) 6 References Cited 3,212,918 10/1965 Tsuet a1. 117-54 UNITED STATES PATENTS 3,420,644 1/1969 Llrones 6526 X10/1894 Barr X WILLIAM D. MARTIN, Prlmary Fixarmner 6 Garratt 5Asslstant Examlner 6/ 1951 Smith 65- 26 U.S. Cl. X.R. 9/1959 McDufiee6524 X 117-88, 54, 123, 167; 6526, 24

